Memory cache sharing in hybrid hard disk

ABSTRACT

A system allows one or more hybrid hard disks or any other storage devices to share a logical nonvolatile device formed by one or more non-volatile memory devices. The system comprises a control logic to reserve on a hybrid hard disk a space that corresponds to a non-volatile memory device in the hybrid hard disk and to use a space access instruction to access the non-volatile memory device. The control logic accesses the logical non-volatile memory device in an event that a content of a storage device is stored in the logical non-volatile memory device in response to an instruction to access the storage device.

BACKGROUND

Hybrid hard disks may integrate non-volatile memory device such as flashmemories into the hybrid hard disks to support read or write caching andburst read mode. However, in redundant arrays of independent disks(RAID) environment, integrated non-volatile memory devices may bebundled into individual hybrid hard disk and they may not be utilized byRAID in a more effective way. For example, a first non-volatile memorydevice in a first hybrid hard disk is isolated from a secondnon-volatile memory device in second hybrid hard disk and can not beshared by the second hybrid hard disk. A non-volatile memory device maystore logical data that may be image of raw data on the hybrid harddisk. Redundancy brought by a RAID system may cause unnecessaryredundancy of non-volatile memory devices inside hybrid hard disks. Forexample, in a RAID 1 or 0+1 implementation, one or more non-volatilememory devices may be wasted. For other multiple hard disk systems, innormal situation, a majority of system loading at a time may be on onehard disk only. In such a situation, non-volatile memory devices on anidle disk may be wasted as well.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention described herein is illustrated by way of example and notby way of limitation in the accompanying figures. For simplicity andclarity of illustration, elements illustrated in the figures are notnecessarily drawn to scale. For example, the dimensions of some elementsmay be exaggerated relative to other elements for clarity. Further,where considered appropriate, reference labels have been repeated amongthe figures to indicate corresponding or analogous elements.

FIG. 1 illustrates an embodiment of a computing device.

FIG. 2 illustrates an embodiment of a physical view of utilization ofnon-volatile memories among one or more hard disks.

FIG. 3 illustrates an embodiment of a logical view of the utilization ofnon-volatile memories of FIG. 2.

FIG. 4 illustrates an embodiment of a control unit that may controlaccess to one or more hard disks.

FIG. 5 illustrates an embodiment of a method that may be used to preparedata or any other information from a hard disk to a cache.

FIG. 6 illustrates an embodiment of a method that may be used to readdata or any other information from a hard disk.

FIG. 7 illustrates an embodiment of a method that may be used to readdata or any other information from a hard disk bypassing a cache.

FIG. 8 illustrates an embodiment of a method that may be used to writedata or any other information to a hard disk.

FIG. 9 illustrates an embodiment of a method that may be used to writedata or any other information to a hard disk bypassing a cache.

DETAILED DESCRIPTION

The following description describes techniques to utilize one or morenon-volatile memories in a hybrid hard disk environment. Theimplementation of the techniques is not restricted in hybrid hard diskenvironment; it may be used by any execution environments for similarpurposes. In the following description, numerous specific details suchas logic implementations, opcodes, means to specify operands, resourcepartitioning/sharing/duplication implementations, types andinterrelationships of system components, and logicpartitioning/integration choices are set forth in order to provide amore thorough understanding of the present invention. However, theinvention may be practiced without such specific details. In otherinstances, control structures and full software instruction sequenceshave not been shown in detail in order not to obscure the invention.

References in the specification to “one embodiment”, “an embodiment”,“an example embodiment”, etc., indicate that the embodiment describedmay include a particular feature, structure, or characteristic, butevery embodiment may not necessarily include the particular feature,structure, or characteristic. Moreover, such phrases are not necessarilyreferring to the same embodiment. Further, when a particular feature,structure, or characteristic is described in connection with anembodiment, it is submitted that it is within the knowledge of oneskilled in the art to effect such feature, structure, or characteristicin connection with other embodiments whether or not explicitlydescribed.

Embodiments of the invention may be implemented in hardware, firmware,software, or any combination thereof. Embodiments of the invention mayalso be implemented as instructions stored on a machine-readable medium,which may be read and executed by one or more processors. Amachine-readable medium may include any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputing device). For example, a machine-readable medium may includeread only memory (ROM); random access memory (RAM); magnetic diskstorage media; optical storage media; flash memory devices; electrical,optical, acoustical or other forms of propagated signals (e.g., carrierwaves, infrared signals, digital signals, etc.), and others.

An example embodiment of a computing device 100 is shown in FIG. 1. Thecomputing device 100 may comprise one or more processors 110 coupled toa chipset 120. The chipset 120 may comprise one or more integratedcircuit packages or chips that couple the processor 110 to system memory130, storage device 140, and one or more I/O devices 150 such as, forexample, mouse, keyboard, video controller, etc. of the computing device100.

Each processor 110 may be implemented as a single integrated circuit,multiple integrated circuits, or hardware with software routines (e.g.,binary translation routines). The processor 110 may perform actions inresponse to executing instructions. For example, the processor 110 mayexecutes programs, performs data manipulations and control tasks in thecomputing device 100. The processor 110 may be any type of processoradapted to execute instructions from memory 130, such as amicroprocessor, a digital signal processor, a microcontroller, oranother processor.

The memory 130 may comprise one or more different types of memorydevices such as, for example, dynamic random access memory (DRAM)devices, static random access memory (SRAM) devices, read-only memory(ROM) devices, and/or other volatile or non-volatile memory devices. Thememory 130 may store instructions and codes represented by data signalsthat may be executed by processor 110.

The chipset 120 may comprise a memory controller 160 that may controlaccess to the memory 130. While FIG. 1 illustrates that memory 130 maycouple to the processor 110 via the chipset 120, in some embodiments,memory 130 may be coupled to the processor 110 directly and the memorycontroller 160 may locate in the processor 110. The chipset 120 mayfurther comprise a storage device interface (not shown) that may accessthe storage device 140. The storage device 140 may comprise a tape, ahard disk drive, a floppy diskette, a compact disk (CD) ROM, a flashmemory device, other mass storage devices, magnetic or optic storagemedia, or any other storage media. The storage device 140 may storeinformation, such as code, programs, files, data, applications, andoperating systems. The chipset 120 may further comprise one or more I/Ointerfaces (not shown) to access the I/O device 160 via buses 112 suchas, for example, peripheral component interconnect (PCI) buses,accelerated graphics port (AGP) buses, universal serial bus (USB) buses,low pin count (LPC) buses, and/or other I/O buses.

The I/O device 160 may include any I/O devices to perform I/O functions.Examples of the I/O device 160 may include controller for input devices(e.g., keyboard, mouse, trackball, pointing device), media card (e.g.,audio, video, graphics), network card, and any other peripheralcontrollers.

FIG. 2 illustrates an embodiment to utilize non-volatile memories in asystem 200 that may comprise one or more hybrid hard disks. In oneembodiment, system 200 may comprise a first hybrid hard disk 220, asecond hybrid hard disk 230 and a normal hard disk 240; however, in someembodiments, the system 200 may comprise a different number of hybridhard disks and normal hard disks or any other storage devices. The firsthybrid hard disk 220 may comprise a first flash memory cache 222 and thesecond hybrid hard disk 230 may comprise a second flash memory cache232; however, other embodiments may comprise a different number of flashmemory caches or any other non-volatile memory devices such as phasechange memory (PCM) or battery backed-up static random access memory(SRAM).

Referring to FIG. 3, logically, the first flash memory cache 222, thesecond flash memory cache 232 and a flash memory 260 that may beaccessible by the control logic 210 may form a logical flash memorycache 250. The logical flash memory cache 250 may be used to storelogical data 226 in the first flash memory cache 222, the second flashmemory cache 232, and/or the flash memory cache 260. For example, theflash memory 260 may be physically on the same board where control logic210 locates; however, in some embodiments, the flash memory 260 maylocate at any other place that may be accessed by the control logic 210.While FIG. 4 illustrates the flash memory 260, in some embodiments, anyother non-volatile memory devices may be utilized, such as PCM, batterybacked-up SRAM.

FIG. 4 is a block diagram that illustrates an embodiment of controllogic 210. In one embodiment, control logic 210 may be coupled with adisk access module 410 to control an access of disk access module 410 toone or more hard disks such as 220, 230 or 240 and one or morenon-volatile memory devices such as 250. The disk access module 410 maybe coupled to a processor (not shown). In one embodiment, the diskaccess module 410 may communicate with the control logic 210 to accessone or more hard disks such as 220, 230 or 240 and/or one or morenon-volatile memory devices such as 250 in response to an instructionfrom the processor. For example, the disk access module 410 may beprovided on a chipset; however, in some embodiments, the disk accessmodule 410 may be implemented in an operating system.

In one embodiment, control logic 210 may reserve a disk space on ahybrid hard disk that may have a size equal to a size of a flash memorycache of the hybrid hard disk. In one embodiment, control logic 210 maypin a block of the disk space to a block of a flash memory cache on thehybrid hard disk. In another embodiment, control logic 210 may use ahard disk interface command or instruction to access the flash memorycache. For example, control logic 210 may generate unmovable systemfiles to reserve the disk space. In another embodiment, control logic210 may hide the disk space to, e.g., an operating system or a computingdevice to reserve the disk space. Referring to FIG. 4, in oneembodiment, control logic 210 may reserve on the first hybrid hard disk220 a first disk space 432 that may comprise a first set of one or moreblocks. A number of blocks in the first set may equal to a number ofblocks of the first flash memory cache 222. Each reserved block in thefirst set may correspond to a block of the first flash memory cache 222.Similarly, control logic 210 may reserve on the second hybrid hard disk230 a second disk space 433 that may have a size equal to that of thesecond flash memory cache 232. Each reserved block on the second hybridhard disk 230 may correspond to a block of the second flash memory cache222.

In another embodiment, control logic 210 may access a block of firstflash memory cache 220 by an instruction to access a corresponding blockof the first reserved space 432. Similarly, control logic 210 may accessa block of second flash memory cache 230 by an instruction to access acorresponding block of the second disk space 434. In another embodiment,referring to FIG. 3, control logic 210 may access the first hybrid harddisk 220 except the first disk space 432, the second hybrid hard disk230 except the second disk space 434 and/or the normal hard disk 240 toread and/or write raw data 224, 234 and/or 244, respectively. In anotherembodiment, control logic 210 may convert raw data, e.g., 224, 234 and244 into logical data, such as 226 in response to disk access module 410requesting for logical data. In one embodiment, control logic 210 maystore logical data 226 into one or more blocks of the logical flashmemory cache 250. In another embodiment, control logic 210 may accessthe logical flash memory cache 250 to read and/or write logical data226. In one embodiment, control logic 210 may use a cache algorithm toallocate a cache block for each hard disk based on utilization. In oneembodiment, control logic 210 may convert raw data into logical datathat may be the same as the raw data in response to disk access module410 requesting for raw data.

In logic, the first flash memory cache 222, the second flash memorycache 232 and a flash memory 260 that may be accessible by the controllogic 210 may form a logical flash memory cache 250, as shown in FIG. 4.Referring to FIG. 4, a cache mapping table 450 may show correspondencebetween a cache block of the logical flash memory cache 250 and a blockof the first flash memory cache 222, the second flash memory cache 232or the flash memory 260. Referring to FIG. 4, entry 452 may representthat cache block Z1 of the logical flash memory cache 250 may correspondto block Y1 of the first flash memory cache 222. Entry 454 may representthat cache block Z2 may correspond to block Y2 of the first flash memorycache 222. Entry 456 may represent that cache block Z3 may correspond toblock Y3 of the second flash memory cache 232. Entry 458 may representthat cache block Z4 may correspond to block Y4 of the flash memory 260.While FIG. 4 illustrates the cache mapping table 450, in someembodiments, any other mapping relationship may be utilized. In oneembodiment, the cache mapping table 450 may be stored in a volatile ornon-volatile memory device that may be accessible by the control logic210. In another embodiment, the cache mapping table 450 may beaccessible by the control logic 210 and may be implemented in softwaresuch as an operating system, hardware such as in chipset or any othercomponent, or firmware. While FIG. 4 illustrates the cache mapping table450, in some embodiments, any data structure such as array or list maybe utilized.

Referring to FIG. 4, control logic 210 may comprise a cache managementmodule 422 and a cache access module 424. In one embodiment, the cachemanagement module 422 may be coupled with the disk access module 410 andmay execute one or more access instruction from the disk access module410 that may be issued by a processor (not shown) coupled to the diskaccess module 410. Cache management module 410 may instruct cache accessmodule 424 to access one or more hard disks 220, 230 or 240 and/or theflash memory 260 in response to an access instruction from the diskaccess module 410. In another embodiment, cache management module 422may access a cached content table 440. In one embodiment, the cachedcontent table 440 may illustrate content that are cached or stored in acache block of the logical flash memory cache 250; however, in someembodiments, any data structure such as array or list may be utilized.

For example, as shown in FIG. 4, entry 442 may represent that content ofblock X1 of the first hybrid hard disk 220 has been stored in block Z1of the logical flash memory cache 250. In another embodiment, entry 444may represent that content of block X2 of the second hybrid hard disk230 has been stored in block Z2 of the logical flash memory cache 250.Entries 446 and 468 may represent that block Z3 and Z4 of the logicalflash memory cache 250 comprise content of block X3 and block X4 of thenormal hard disk 240, respectively. While FIG. 4 illustrates the cachedcontent table 440, in some embodiments, any other content may be storedin a cache block. In one embodiment, the cached content table 440 may bestored in a volatile or non-volatile memory device that may beaccessible by the control logic 210. In another embodiment, the cachedcontent table 440 may be accessible by the control logic 210 and may beimplemented in software, e.g., in an operating system, hardware such asin chipset or any other component, or firmware.

Referring to FIG. 5, it is illustrated an embodiment of a method thatmay be used by cache management module 422 to prepare or read data fromthe first hybrid hard disk 220, the second hybrid hard disk 230 and thenormal hard disk 240 to the logical flash memory cache 250 inbackground, e.g., based on a PrepareBlock instruction from disk accessmodule 410. In box 502, cache management module 422 may obtain a number(e.g., which may be represented by BlockCount) of a set of one or moredisk blocks to be prepared into the logical flash memory cache 250 and alist of the set of blocks from the PrepareBlock instruction. In diamond504, cache management module 422 may determine if BlockCount is biggerthan a number (e.g., which may be represented by TotalCache) of totalcache blocks in the logical flash memory cache 250. In response todetermining that BlockCount is bigger than TotalCache, cache managementmodule 422 may return “unsuccessful” or any other indicator such asnumber or logical value to a processor that has issued the PrepareBlockinstruction (box 506). In response to determining that BlockCount is nobigger than TotalCache, cache management module 422 may let a variable,e.g., BlockToGet, equal to BlockCount (box 508). In one embodiment,variable BlockToGet may represent a number of cache blocks that are tobe obtained by cache management module 422.

In diamond 510, cache management module 422 may determine if cacheaccess module 422 may successfully obtain BlockToGet cache blocks fromthe logical flash memory cache 250. If it is determined that the cacheaccess module 422 may successfully obtain BlocktoGet cache blocks fromthe logical flash memory cache 250, in box 512, cache management module422 may instruct cache access module 424 to perform a ReadDiskToCacheinstruction. In response to receiving the ReadDiskToCache instruction,cache access module 424 may read in background content of a disk blockfrom the list obtained in box 502 to a cache block that can besuccessfully obtained and may clear out a dirty flag that may correspondto the cache block.

In contrast, in response to determining that cache access module 424fails to obtain BlockToGet cache blocks, cache management module 422 maydetermine one or more cache blocks to be released in the logical flashmemory cache 250 based on a cache replacement algorithm such as leastrecent used (LRU), most recently used (MRU) or any other cachereplacement algorithm (box 514). In one embodiment, cache managementmodule 422 may release a cache block to be released that is not dirty.In another embodiment, in box 516, from the cache blocks determined tobe released in box 514, for a cache block that is dirty or whose contentis inconsistent with content of a disk block that corresponds to thecache block as shown in cached content table 440, cache managementmodule 422 may transmit, e.g., a WriteCacheToDisk instruction to cacheaccess module 424 to release the dirty cache block. In one embodiment,cache management module 422 may determine that a cache block is dirtybased on a dirty flag that may be comprised in the cache block or cachedcontent table 440 or any other data structure. In another embodiment,cache management module 422 may compare content of a cache block andcontent of a corresponding disk block indicated by cached content table440 and may determine that the cache block is dirty in response todetermining that the two contents are different. In one embodiment, thecache access module 424 may write content of the dirty cache block tothe corresponding disk block and may clear out a dirty flag of the dirtycache block in response to the WriteCacheToDisk instruction.

In box 518, cache management module 422 may instruct cache access module424 (e.g., by a ReadDiskToCache instruction) to read content of a diskblock from the list obtained in box 502 to a cache block obtained in box514 and to clear out a dirty flag that may correspond to the cacheblock. In another embodiment, cache management module 422 may furtherupdate cached content table 440. In box 520, cache management module 422may let BlockToGet=BlockToGet−a number (e.g., which may be representedby BlockRead) of blocks that have been read in boxes 512 and 518. Indiamond 522, cache management module 422 may determine if BlockToGet=0.In box 524, cache management module 422 may return e.g., “successful” toa processor that has issued the PrepareBlock instruction, in response todetermining that BlockToGet equals to zero. In contrast, in response todetermining that BlockToGet is bigger than zero or does not equal tozero, the flow may return to diamond 510.

Referring to FIG. 6, it is illustrated an embodiment of a method thatmay be used by cache management module 422 to read data from hard disks220, 230 and/or 240, e.g., based on a ReadBlock instruction from diskaccess module 410. In box 602, block management module 422 may obtain anumber of disk blocks to be read, e.g., Block Count, and a list of thedisk blocks based on the ReadBlock instruction. In box 604, cachemanagement module 422 may let a variable, e.g., BlockToRead, equal toBlockCount. In diamond 606, cache management module 422 may determine ifa disk block to be read has already been cached in the logical flashmemory cache 250. For example, cache management module 422 may look up acache block of the logical flash memory cache 250 that has storedcontent of a disk block to be read in the cached content table 440. Inresponse to determining that the disk block has been cached in thelogical flash memory cache 250, e.g., the corresponding cache block hasbeen found, cache management module 422 may instruct (e.g., by aReadFromCache instruction) cache access module 424 to read content ofthe cache block and to pass the content to cache management module 422(box 608). In one embodiment, cache access module 424 may use a directmemory access (DMA) method or any other method to pass the content or areference to the content to cache management module 422.

In contrast, in response to determining that content of a disk block tobe read is not cached or absent in the logical flash memory cache 250,cache management module 422 may allocate a cache block of the logicalflash memory cache 250 to the disk block (box 610). In one embodiment,cache management module 422 may allocate a blank cache block to a diskblock to be read, e.g., by a cache allocation algorithm. In anotherembodiment, cache management module 422 may allocate a cache block to bereleased (e.g., not dirty) to a disk block to be read. In yet anotherembodiment, for a dirty cache block that is determined to be released,in response to a WriteCacheToDisk instruction from cache managementmodule 422, cache access module 424 may write content of a dirty cacheblock to a corresponding disk block as indicated by cached content table440 and may clear out a dirty flag of the cache block to allocate thedirty cache block to a disk block to be read.

In box 612, cache management module 422 may transmit a ReadDiskToCacheinstruction to cache access module 424 to instruct cache access module424 to read content of a disk block to be read to a cache blockallocated for the disk block in box 610 in background and to clear out adirty flag of the cache block. In box 614, cache management module 422may instruct cache access module 424 (e.g., by a ReadFromCacheinstruction) to read content of a cache block allocated in box 610 andto pass the content or a reference to the content to cache managementmodule 422 by, e.g., a DMA or any other method. The descriptions toboxes 616, 618 and 620 may refer to the descriptions on boxes 520, 522and 524, respectively.

Referring to FIG. 7, it is illustrated an embodiment of a method thatmay be used by cache management module 422 to read data from hard disks220, 230 and/or 240 and may bypass the logical flash memory cache 250,e.g., based on a ReadThruBlock instruction from disk access module 410.In box 702, block management module 422 may obtain a number of diskblocks to be read, e.g., Block Count, and a list of the disk blocks fromthe ReadThruBlock instruction. Description on box 704 may refer to thedescription on box 604. In diamond 706, cache management module 422 maydetermine if a disk block to be read is cached in the logical flashmemory cache 250 based on cached content table 440. In box 708, inresponse to determining that the disk block is cached in the logicalflash memory cache 250, cache management module 422 may instruct (e.g.,by a ReadFromCache instruction) cache access module 424 to read contentof a cache block that corresponds to the cached disk block and to passthe content or a reference to the content to the cache management module422 by a DMA method or any other method. In contrast, in box 710, inresponse to determining that the disk block is not cached or absent inthe logical flash memory cache 250, cache management module 422 mayinstruct cache access module 424 (e.g., by a ReadThruDisk instruction)to read content from the disk block. In one embodiment, cache accessmodule 424 may bypass the logical flash memory cache 250 to access thedisk block directly.

In box 712, cache management module 422 may letBlockToRead=BlockToRead−a number (e.g., which may be represented byBlockRead) of blocks that have been read in boxes 708 and 710. Indiamond 714, cache management module 422 may determine if BlockToRead=0.In box 716, cache management module 422 may return e.g., “successful” toa processor that has issued the ReadThruBlock instruction, in responseto determining that BlockToRead equals to zero. In contrast, in responseto determining that BlockToRead is bigger than zero or does not equal tozero, the flow may return to box 710.

FIG. 8 illustrates an embodiment of a method that may be used by cachemanagement module 422 to write data to hard disks 220, 230 and/or 240,e.g., based on a WriteBlock instruction from disk access module 410. Inbox 802, cache management module 422 may obtain a number (e.g., whichmay be represented by BlockCount) of a set of one or more blocks to bewritten to disk blocks and a list of the set of blocks from theWriteBlock instruction. In diamond 804, cache management module 422 maylet a variable, e.g., BlockToWrite, equal to BlockCount.

In diamond 806, cache management module 422 may determine if a diskblock to be written has already been cached in the logical flash memorycache 250. If it is determined that the disk block is cached in thelogical flash memory cache 250, in box 812, cache management module 422may pass a block of data to be written or a reference of the data suchas index, pointer or address to the cache access module 424 and instructcache access module 424 (e.g., by a WriteToCache instruction) to writethe data to a cache block that corresponds to the disk block based onthe cached content table 440 and to set a dirty flag of the cache block.In one embodiment, cache access module 424 may use DMA or any othermethod to write the block of data to the cache block.

In contrast, in response to determining that the disk block is notcached or absent in the logical flash memory cache 250, cache managementmodule 422 may allocate a cache block to the disk block (box 810). Amethod to allocate a cache block may similar to the description on box610. In box 812, cache management module 422 may instruct cache accessmodule 424 to write the block of data to be written to a cache blockallocated in box 810 and to set a dirty flag of the cache block, e.g.,by a WriteToCache instruction. In one embodiment, cache access module424 may use DMA or any other method to write the block of data to thecache block.

In box 814, cache management module 422 may letBlockToWrite=BlockToWrite−a number (e.g., which may be represented byBlockWrite) of blocks that have been written in boxes 808 and 812. Indiamond 816, cache management module 422 may determine ifBlockToWrite=0. In response to determining that BlockToWrite is biggerthan zero or does not equal to zero, the flow may return to diamond 806.In contrast, in box 818, cache management module 422 may determine if itis to flush out cache data. For example, cache management module 422 maydetermine if there is any dirty cache block in the logical flash memorycache 250. In box 820, in response to determining that it is to flushout cache data, e.g., a dirty cache block or a dirty flag of a cacheblock is found, cache management module 422 may instruct cache accessmodule 424 to write content of a cache disk that is written in box 812or 816 to a correspond disk block, e.g., by a WriteCacheToDiskinstruction and to clear out a dirty flag of the cache block. Incontrast, in box 822, cache management module 422 may return e.g.,“successful” or any other indicator.

Referring to FIG. 9, it is illustrated an embodiment of a method thatmay be used by cache management module 422 to write data to hard disks220, 230 and/or 240 and may bypass the logical flash memory cache 250,e.g., based on a WriteThruBlock instruction from disk access module 410.The descriptions on boxes 902, 904, 906 may refer to the descriptions onboxes 802, 804, 806, respectively. For example, in block 902, cachemanagement module 422 may obtain a list of blocks of data to be writtento hard disks 220, 230 and/or 240 based on the WriteThruBlockinstruction. A number of blocks in the list may be represented byBlockCount. In diamond 906, cache management module 422 may determine ifa disk block to be written is cached in the logical flash memory cache250 based on cached content table 440. In box 908, in response todetermining that the disk block is cached in the logical flash memorycache 250, cache management module 422 may instruct cache access module424 to write a block of data to be written to the cached disk block andto set a dirty flag of a cache block that corresponds to the disk block,e.g., by a WriteToCache instruction. In box 916, cache management module422 may instruct cache access module 424 to write content in the cacheblock that is written in box 914 to the cached disk block and to clearout a dirty flag set in box 914, e.g., by a WriteCacheToDiskinstruction. In contrast, in box 912, in response to determining thatthe disk block is not cached or absent in the logical flash memory cache250, cache management module 422 may instruct cache access module 424 towrite the block of data from cache management module 422 to the diskblock, e.g., by a WriteThruDisk instruction. In one embodiment, cacheaccess module 424 may bypass the logical flash memory cache 250 toaccess the disk block directly.

In box 918, cache management module 422 may letBlockToWrite=BlockToWrite−a number (e.g., which may be represented byBlockWrite) of blocks that have been written in boxes 912 and 914. Indiamond 920, cache management module 422 may determine ifBlockToWrite=0. In box 922, cache management module 422 may return e.g.,“successful” or any other indicator, in response to determining thatBlockToWrite equals to zero. In contrast, in response to determiningthat BlockToWrite is bigger than zero or does not equal to zero, theflow may return to diamond 906.

In one embodiment, cache management module 422 may execute a FlushCacheinstruction in response to a dirty cache block of the logical flashmemory cache 250 being found. For example, for the FlushCacheinstruction, cache management module 422 may call a WriteCahceToDiskinstruction. In response to receiving the WriteCahceToDisk instruction,cache access module 422 may write a dirty cache block to a disk blockthat corresponds to the dirty cache block based on cached content table440 and clear out a dirty flag of the cache block. In anotherembodiment, the cache access module 424 may execute, e.g., aInitCacheList instruction to check inventory of one or more availablecaches and may build a cache mapping list 450 in response to a requestfrom a processor such as system bootup. In another embodiment, inasynchronous mode, cache access module 424 may execute aQueryCommandStatus instruction to return a status that may indicatecompleteness of one or more instructions such as instructions to thecache management module 422.

While the methods of FIGS. 5-9 are illustrated as a sequence ofoperations, the illustrated operations may be performed in a differentorder in other embodiments. For example, while FIGS. 5-9 illustrateboxes 520, 522, 616, 618, 712, 714, 814, 816, 918, 920, respectively;however, in some embodiments, the boxes may be omitted. In anotherembodiment, one or more hard disk interface commands or instructions maybe used to execute one or more instructions such as ReadThroughDisk,ReadDiskToCache, WrtieThruDisk, WriteCacheToDisk. In another embodiment,control logic 210 and/or access disk access module 410, cache managementmodule 422 or cache access module 424 may be implemented in hardware,software, and/or firmware or any combination thereof.

In another embodiment, the cached content table 440 may be updated inresponse to a cache block being written. In some embodiments, the flowof FIG. 6 may proceed to box 610 in response to determining thatBlockToRead is not equal to zero in diamond 618. Similarly, the flow ofFIG. 8 may proceed from diamond 816 to box 810 or the flow of FIG. 9 mayproceed from diamond 920 to box 914, if BlockToWrite is not equal tozero. In another embodiment, the flow of FIG. 7 may proceed to diamond706 if BlockToRead is not equal to zero in diamond 714. While FIG. 4illustrates control logic 210 to comprise cache management module 422and cache access module 424, in some embodiments, the functions ofcontrol logic 210 may be implemented in one or more blocks anddistributed among the blocks. While FIG. 4 illustrates to comprise twohybrid hard disks, a normal hard disk and a flash memory, in someembodiments, a hybrid hard disk may share a non-volatile memory devicein the hybrid hard disk with a storage device. In another embodiment,two hybrid hard disks may share a non-volatile memory device in eachhybrid hard disk with each other. In yet another embodiment, twonon-volatile memory devices may form a logical non-volatile memorydevice that can be used to store content on a storage device. In yetanother embodiment, a first non-volatile memory device and a secondnon-volatile memory device in a hybrid hard disk may form a logicalnon-volatile memory device that can be used to store content on thehybrid hard disk.

While certain features of the invention have been described withreference to embodiments, the description is not intended to beconstrued in a limiting sense. Various modifications of the embodiments,as well as other embodiments of the invention, which are apparent topersons skilled in the art to which the invention pertains are deemed tolie within the spirit and scope of the invention.

1. A system, comprising: a processor; a control logic to access a firstnon-volatile memory device in an event that a content of a storagedevice is stored in the first non-volatile memory device in response toa first instruction to access the storage device from the processor. 2.The system of claim 1, wherein: the first non-volatile memory device isprovided on a first hybrid hard disk, the control logic to reserve onthe first hybrid hard disk a space that corresponds to the firstnon-volatile memory device and to use a space access instruction toaccess the first non-volatile memory device.
 3. The system of claim 1,wherein: the storage device comprises a first hybrid hard disk thatcomprises a second non-volatile memory device, the control logic toreserve on the first hybrid hard disk a space that corresponds to thesecond non-volatile memory device and to use a space access instructionto access the second non-volatile memory device.
 4. The system of claim1, wherein the control logic to access a second non-volatile memorydevice in an event that the content of the storage device being storedin the second non-volatile memory device based on the first instruction.5. The system of claim 1, wherein: the first non-volatile memory deviceis provided on a first hybrid hard disk, the storage device comprises asecond hybrid hard disk that comprises a second non-volatile memorydevice.
 6. The system of claim 5, wherein: the control logic to accessthe second non-volatile memory device in an event that a content of thefirst hybrid hard disk is stored in the second non-volatile memorydevice in response to the first instruction.
 7. A method, comprising:reserving on a first hybrid hard disk a space that corresponds to afirst non-volatile memory device on the first hybrid hard disk, inresponse to a first instruction to access the storage device, accessingthe first non-volatile memory device in the event that a content of astorage device being stored in the first non-volatile memory device viaa space access instruction.
 8. The method of claim 7, wherein thestorage device comprises a second hybrid device that comprises a secondnon-volatile memory device, wherein the method comprises in response toa second instruction to access the first hybrid hard disk, accessing thesecond non-volatile memory device in the event that a content of thefirst hybrid hard disk being stored in the second non-volatile memorydevice.
 9. The method of claim 7, comprising: in response to the firstinstruction, allocating a first block of the first non-volatile memorydevice to a second block of the storage device in the event that acontent of the second block is absent in the first non-volatile memorydevice, storing the content of the second block to the allocated firstblock.
 10. The method of claim 7, comprising: in response to the firstinstruction, allocating a first block of the first non-volatile memorydevice to a second block of the storage device in the event that acontent of the second block is absent in the first non-volatile memorydevice, accessing the allocated first block to write a content comprisedin the first instruction in the first block.
 11. The method of claim 7,wherein the storage device comprises a second hybrid device thatcomprises a second non-volatile memory device, wherein the methodcomprises forming a logical non-volatile memory device by the firstnon-volatile memory device and the second non-volatile memory device toshare the logical non-volatile memory device among the first hybrid harddisk and the second hybrid hard disk.
 12. The method of claim 7,comprising: in response to the first instruction, allocating a firstblock of the first non-volatile memory device that corresponds to asecond block of the storage device in the event that a content of thesecond block is absent in the first non-volatile memory, writing acontent comprised in the first instruction to the first block, andupdating the second block based on the first block.
 13. A machinereadable medium comprising a plurality of instructions that in responseto being executed result in a computing device forming a logicalnon-volatile memory device by a first non-volatile memory device and asecond non-volatile memory device, accessing the logical non-volatilememory device in response to determining that a content of a storagedevice is stored in the logical non-volatile memory device based on aninstruction to access the storage device.
 14. The machine readablemedium of claim 13, further comprising a plurality of instructions thatin response to being executed result in a computing device allocating afirst block of the logical non-volatile device to a second block of thestorage device in the event that a content of the second block is absentin the logical non-volatile memory device in response to theinstruction, and accessing the first block to store the content of thesecond block.
 15. The machine readable medium of claim 13, wherein thestorage device comprises a first hybrid disk that comprises the firstnon-volatile memory device, the machine readable medium furthercomprising a plurality of instructions that in response to beingexecuted result in a computing device releasing a first block of thelogical non-volatile memory device to store a content of a second blockof the hybrid hard disk.
 16. The machine readable medium of claim 13,further comprising a plurality of instructions that in response to beingexecuted result in a computing device writing a content comprised in theinstruction to a first block of the logical non-volatile memory devicein response to determining that a second block of the storage device iscached in the logical non-volatile memory device, writing the content ofthe first block to the second block.